The present invention relates generally to a pixel structure of an organic light emitting diode (OLED) display and a liquid crystal display (LCD), and more specifically to a pixel structure of a sunlight readable display.
Flat-panel displays have become one of the most important electronic products. Among the flat-panel displays, organic light emitting displays have the advantages of self-light emitting, high luminous efficiency, wide viewing angle, fast response speed, high reliability, full color, low-voltage driving, low power consumption and simple fabrication.
Nowadays, there are many kinds of structures and fabrication methods for passive-drive or active-drive organic light emitting display devices. Although the manufacturing process of a conventional passive-drive organic light emitting display device is simple and manufacturing cost is less expensive, the resolution of the display device manufactured is not high enough. It can only make the displays that have small size and low resolution. On the contrary, an active-drive organic light emitting display device using thin film transistors has the advantages of high resolution, low power consumption and low-voltage driving. However, the contrast ratio of a bright state to a dark state of a conventional organic light emitting diode gets worse under direct sunlight. By increasing the brightness of the organic light emitting diode, higher contrast ratio can be obtained but the power consumption is also increased.
Recently, the market for liquid crystal display panels is growing rapidly. High quality liquid crystal displays are therefore produced. Conventional reflective liquid crystal displays are readable under direct sunlight. However, they need front light source under weak light environment and the pixel quality is worse than that of liquid crystal displays with a back light source and displays with self-light emitting.
Therefore, it is necessary to develop displays with high contrast ratio, low power consumption, self-light emitting and good pixel quality.
This invention has been made to overcome the above-mentioned drawbacks of conventional organic light emitting diode displays and liquid crystal displays. The primary object is to provide a pixel structure of a sunlight readable display. According to the invention, the pixel structure combines a half organic light emitting diode structure and a half reflective liquid crystal display structure so as to have the advantages of both display structures.
The half reflective LCD structure of the invention comprises mainly a glass substrate, a reflective metal layer, a color filter, a liquid crystal layer, a quarter-wave film and a polarizer. The half OLED structure of the invention comprises mainly a glass substrate, a black matrix on the top surface of the glass substrate, a buffer layer on the black matrix, a poly-Si layer on the buffer layer to define the regions of the source and drain electrodes of thin film transistors. A dielectric layer is formed on the poly-Si layer, and a metal gate layer is formed on the dielectric layer to define the region of the gate electrode of a thin film transistor. An intermediate layer is formed on the gate layer, and contact holes are formed in the intermediate layer. A metal layer covers the intermediate layer and a first passivation layer is formed on top of the metal layer. A layer of transparent material is formed on a portion of the passivation layer and defined as an anode layer, and a layer of OLED material is formed on the layer of transparent material and the first passivation layer. A transparent cathode layer is formed on a portion of the layer of the OLED material. A second dielectric layer is then deposited to cover the transparent cathode layer as well as the first dielectric layer, and an ITO pixel electrode layer is formed on the second dielectric layer.
There are two preferred embodiments in the invention. In the first preferred embodiment, the reflective metal layer is formed on the color filter. The display is operated at the organic light emitting diode mode when the light path of the display is downward. In the organic light emitting mode, liquid crystal molecules in the liquid crystal layer are operated at a normally black mode. In the second preferred embodiment, the reflective metal layer is formed on the TFT substrate. The display is operated at the organic light emitting diode mode and liquid crystal molecules in the liquid crystal layer are operated at a normally white mode when the light path of the display is upward.
According to the invention, a thin film transistor is used as a switch to solve the problem of crosstalk between the organic light emitting diode mode and the liquid crystal mode as well as the problem of direct current residual.
In addition, data signals in the organic light emitting diode mode and the liquid crystal mode can be controlled by different control systems because the thin film transistor is used as the switch in the display. By properly selecting liquid crystal material and OLED material so that the ranges of the data signals are similar, only one data driver is needed. This saves the cost of the data driver.
The foregoing and other objects, features, aspects and advantages of the present invention will become better understood from a careful reading of a detailed description provided herein below with appropriate reference to the accompanying drawings.